AC drive discharge type display apparatus

ABSTRACT

An AC drive discharge type display apparatus which includes a display panel having groups of transverse electrodes and vertical electrodes which are positioned in cross form with a gap therebetween and having cross points which are made luminescent by applying an AC sustaining drive voltage, a turn-on signal and a turn-off signal. A drive circuit is further provided and has transistors and resistances which are connected at one end to the collector electrode of the transistor and the other end of the resistor being disposed in a matrix; means for commonly connecting said other ends of the resistors in each transverse line of the matrix; a first selective switch circuit for applying the turn-on signal or the turn-off signal by selectively driving the transverse lines which are commonly connected; means for commonly connecting the bases and emitters of the transistors in a vertical line of the matrix; means for connecting each of the bases and emitters which are commonly connected, through a diode to the sustaining drive voltage source; a second selective switch circuit for selectively driving the vertical lines by connecting the same to the bases or emitters which are commonly connected; and wherein the collectors of the transistors of the drive circuit are connected to the electrodes in one or both of the groups of the electrodes in the transverse or vertical direction of the display panel.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to an AC drive discharge type display apparatus and more particularly to an AC drive discharge type display apparatus having a drive circuit for applying a sustaining drive voltage, a turn-on pulse and a turn-off pulse to a matrix type display panel.

2. Description of the Prior Art

FIGS. 1a and 1b are respectively a partially broken schematic view of one embodiment of a display panel used for a conventional AC drive discharge type display apparatus, wherein the reference 1 designates a glass plate; 2 designates linear electrodes; 3 designates an insulation layer, 4 designates a discharge gap; and 5 designates a spacer.

In the display panel, the two sheets of glass plates 1 having the plurality of linear electrodes 2 on which the insulation layer 3 is placed, are formed with the discharge gap of fixed length by the spacer 5 so as to cross the linear electrodes 2 of each sheet.

The cross points of the linear electrodes 2 of the display panel are respectively luminescent dots which can be separately turned-on or turned-off. The luminescent dots provide the picture elements for display.

In the drawings, like reference numerals designate identical or corresponding parts throughout the several views. FIGS. 2a-2c are diagrams of waveforms for illustrating the various states of voltage application during the time of driving of the discharge panel, wherein the reference numeral 6 designates a sustaining drive voltage; 7 designates a turn-on pulse; 8 designates a luminescent pulse; and 9 designates a turn-off pulse. The operation of the display panel of FIGS. 1 a and 1b will be explained by referring to FIGS. 2a-2c.

In order to drive the display panel, the AC sustaining drive voltage 6 of FIG. 2 a is applied, in a normal state, across the discharge gap 4 through the two groups of the linear electrodes 2. The turn-on pulse 7 which has a level higher than the discharge initiation voltage V_(f) is applied between the two linear electrodes 2 crossed at the turn-on point at the time of turn-on, whereby a discharge results only at the cross point. Once the discharge occurs, the luminescence is intermittently maintained until the turn-off pulse 9 of FIG. 2a is applied. Hereinafter, one group of the linear electrodes 2 in the two groups is referred to as X electrodes (X drive lines) and the other group is referred as Y electrodes (Y drive lines).

In order to apply the voltages of FIG. 2 a, i.e. the sustaining drive voltage 6, the turn-on pulse 7 and the turn-off pulse 9 across the discharge gap 4, the voltage of FIG. 2 b which is the sustaining drive voltage 6a, the turn-on pulse 7a and the turn-off pulse 9a is applied to the X electrodes and the voltage of FIG. 2c which is the sustaining drive voltage of FIG. 2c which is the sustaining drive voltage 6b, the turn-on pulse 7b and the turn-off pulse 9b is applied to the Y electrodes.

Incidentally, the turn-on pulses 7a and 7b respectively have a level of one-half of that of the turn-on pulse 7, and have reverse polarities to each other. The turn-off pulses 9a and 9b respectively have a level of one-half of that of the turn-off pulse 9 and have reverse polarities to each other.

FIG. 3 is a diagram illustrating one embodiment of the drive circuit for the display panel of the conventional AC drive discharge type display apparatus, wherein V_(s) designates a sustaining drive voltage terminal; V_(p) designates a turn-on voltage terminal; S_(ai) (i = 1,2,3) S_(bj) (j = 1,2,3 ) designate selective switch circuits; and E_(ij) (i,j = 1,2,3) designate output terminals. The drive circuit is a matrix type circuit wherein AND circuits are formed by the resistances and the diodes.

In FIG. 3, nine lines of the linear electrodes 2 (FIGS. 1a and 1b) are given as the X electrodes of the display panel, and accordingly each linear electrode is connected through the respective output terminal E_(ij) to three elements which consists of two diodes D_(a), D_(b) and a resistance R_(a).

In the drive circuit, the sustaining drive voltage 6 having the waveform of FIG. 2b, is applied as an input to the sustaining drive voltage terminal V_(s), and is passed through the diode D_(a) to the output terminal E_(ij) for the X electrode at the charge up time and is then passed at the discharge time through the diode D_(b) and a selective switch circuit S_(bj) of a switch element, e.g. a transistor which is usually in the ON state, to the sustaining drive voltage terminal V_(s).

Incidentally, the selective switch circuit S_(ai) is usually in the OFF state. In order to apply the turn-on pulse shown in FIG. 2b, one switch of the first selective switch circuit S_(ai) which is connected to the turn-on voltage terminal V_(p), is turned on and one switch of the second selective switch circuit S_(bj) is turned off, whereby the turn-on pulse 7a is applied through one terminal of the output terminal E_(ij) to one linear electrode 2 of the X electrodes of the display panel. For example, when the turn-on pulse 7a is applied to the X electrodes which are connected to the output terminals E₂₂, the switch S_(a2) is turned on and the switch S_(b2) is turned off, whereby the current is passed through the three transverse resistances R_(a) which are connected to the switch S_(a2). However, since the switches S_(b1) are in the ON state, the current passing through the vertical lines is passed through the diodes D_(b) and the switches S_(b1), S_(b3) to the sustaining drive voltage terminal V_(s). The voltage of the output terminals E₂₁, E₂₃ is kept at the same level as that of the terminal V_(s) by the voltage drop in the resistance R_(a) and accordingly the turn-on pulse 7a is not applied to the X electrodes which are connected to the output terminals E₂₁, E₂₃ and accordingly the turn-on pulse 7a is applied only to the X electrode which is connected to the output terminal E₂₂ in the line of the switch S_(b2) which is in the OFF state. The selectivity is determined by the characteristic of the AND circuits which consist of the resistance and the diodes. The turn-off pulse 9a (FIG. 2b) can also be applied separately to each of the linear electrodes of the X electrodes in a manner similar to that of the turn-on pulse 7a.

Certain problems exist with the conventional drive circuit for the display panel using the AND circuit system of the resistance and the diode in that disadvantageously a large consumption of power is required, since unnecessary current is passed through the resistance R_(a) to the circuit connected to the linear electrodes 2 to which the turn-on pulse and the turn-off pulse are not applied. Moreover, the conventional drive circuit also disadvantageously requires three circuit elements, namely two diodes D_(a), D_(b) and one resistance R_(a), for each linear electrode 2, and accordingly the number of circuit elements is large.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a new and improved unique AC drive discharge type display apparatus which overcomes the disadvantages of the conventional technology and which decreases the number of circuit elements of the drive circuit and decreases consumption power.

Briefly, in accordance with the present invention, the foregoing and other objects are attained by providing an AC drive discharge type display apparatus which includes a display panel having groups of transverse electrodes and vertical electrodes which are positioned in cross form with a gap therebetween having cross points which are made luminescent by applying an AC sustaining drive voltage, a turn-on signal and a turn-off signal. A drive circuit is further provided and has transistors and resistances which are connected at one end to the collector electrode of the transistor and the other end of the resistor being disposed in a matrix; means for commonly connecting said other ends of the resistors in each transverse line of the matrix; a first selective switch circuit for applying the turn-on signal or the turn-off signal by selectively driving the transverse lines which are commonly connected; means for commonly connecting the bases and emitters of the transistors in a vertical line of the matrix; means for connecting each of the bases and emitters which are commonly connected, through a diode to the sustaining drive voltage source; a second selective switch circuit for selectively driving the vertical lines by connecting the same to the bases or emitters which are commonly connected; and wherein the collectors of the transistors of the drive circuit are connected to the electrodes in one or both of the groups of the electrodes in the transverse or vertical direction of the display panel.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention will become apparent as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIGS. 1a and 1b are respectively a partially broken schematic view and a sectional view of one embodiment of a display panel of the conventional AC drive discharge type display apparatus;

FIGS. 2a, 2b and 2c are waveforms for illustrating the application of voltage to the display panel of FIGS. 1a and 1b;

FIG. 3 is a circuit diagram for illustrating the drive circuit for the display panel of the conventional AC drive discharge type display apparatus;

FIGS. 4, 5 and 6 are respectively circuit diagrams for showing preferred embodiments of display panel drive circuits of the AC drive discharge type display apparatus of the present invention; and

FIG. 7 is a circuit diagram of one embodiment of an input circuit of the drive circuits shown in FIGS. 4-6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, preferred embodiments of the invention will be illustrated.

FIG. 4 is a circuit diagram of one preferred embodiment of a display panel drive circuit of an AC drive discharge type display apparatus according to the present invention wherein T_(ij) (= 1,2,3) (j = 1,2,3) designates a transistor; R₁ and R₂ designate resistances; D_(a) and D_(b) designate diodes and V_(b) designates a bias power source. The drive circuit shown can be used for the X electrodes of the nine linear electrodes 2 (FIGS. 1a and 1b) of the display panel.

The structure of the circuit will be now described as follows. The drive circuit is formed in a matrix using a plurality of the unit circuits each of which consists of one transistor T_(ij) and one resistance R₁ wherein the collector electrode of the transistor T_(ij) in each unit circuit is connected to one end of the resistance R₁ of the unit circuit and the output terminal E_(ij) (i = 1,2,3; j = 1,2,3) to the X electrodes of display panel. The other end of the resistances R₁ of the unit circuits in the transverse line of the matrix are commonly connected to one transverse line which is connected to a first selective switch circuit S_(ai) which is connected to a turn-on voltage terminal V_(p).

On the other hand, the base electrodes of the transistors T_(ij) of the unit circuits in the vertical line of the matrix are commonly connected to one vertical line, each of which is connected to a diode D_(a). The diode D_(a) is connected in the forward direction of the base-emitter junctions of the transistors T_(ij) and to the sustaining drive voltage terminal V_(s). The vertical line is also connected through the resistance R₂ to a second selective switch circuit S_(bj) for selecting the vertical lines of the matrix. The emitter electrodes of the transistor T_(ij) are connected to another vertical line which is connected through a common diode D_(b). The common diode D_(b) is connected in the forward direction of the base emitter junctions of the transistors T_(ij) and to the sustaining drive voltage terminal V_(s). The vertical line is also connected through the common bias power source V_(b) to the second selective switch circuit S_(bj). Incidentally, the bias power source V_(b) is connected in the forward direction of the base-emitter junctions of the transistors T_(ij).

The operation of the drive circuit will now be described as follows. The first selective switch circuit S_(ai) is usually in the OFF state and the second selective switch circuit S_(bj) is usually in the ON state. In these states the sustaining drive voltage 6a (FIG. 2b) is applied as an input to the sustaining drive voltage terminal V_(s). When the positve voltage V_(s) is applied to the terminal V_(s), the positive voltage V_(s) is applied through the diode D_(a) to the base electrode of the transistors T_(ij) since the bias voltage is therefore applied between the base-collector of the transistors in the direction from the base to the collector and the transistors are NPN type, whereby the positive voltage V_(s) which is substantially equal to the base voltage is applied to the collector electrode of the transistor T_(ij), that is connected to the output terminal E_(ij), of the X electrodes of the display panel. When the terminal V_(s) becomes a zero voltage, since the selective switch circuit S_(bj) is in the ON state, the bias voltage is applied through the resistance R₂ between the base-emitter of the transistors T_(ij) by the bias power source in the forward direction to the base emitter junction, whereby the transistor T_(ij) is in the ON state. Accordingly, the positive voltage V_(s) which is substantially equal to the base voltage is applied to the output terminal E_(ij) of the X electrodes of the display panel, that is the collector electrode of the transistor T_(ij). When the terminal V_(s) becomes a zero voltage, the switch circuit S_(bj) is in the ON state and the transistor T_(ij) is in the ON state.

On the other hand, the emitter electrode of the transistors T_(ij) is connected through the diode D_(b) which is connected in the forward direction to the sustaining drive voltage terminal V_(s), whereby the voltage at the output terminals E_(ij) is substantially equal to the voltage at the terminal V_(s) that is the zero voltage.

Thus, a drive waveform having an amplitude substantially equal and level to that of the sustaining drive voltage 6_(a) applied to the terminal V_(s) is applied to the output terminal, that is the X electrodes of the display panel which are connected to the collector electrodes of the transistors T_(ij), when the first selective switch circuit S_(ai) is in the OFF state and the second selective switch circuit S_(bj) is in the ON state and the sustaining drive voltage 6_(a) (FIG. 2b) is applied to the sustaining drive voltage terminal V_(s).

The operation of applying the turn-on pulse 7_(a) to only the output terminal E₂₂ will now be explained. In this case, the turn-on pulse voltage 7_(a) is applied to the turn-on voltage terminal V_(p) and the switches S_(a1), S_(a3) and the switch S_(b2) are in the OFF state and the switch S_(a2) and the switches S_(b1) and S_(b3) are in the ON state, whereby the current resulting from the turn-on pulse voltage is passed through the switch S_(a2) in the ON state and the resistance R₁ to the transistors T_(ij).

On the other hand, the switches S_(b1), S_(b3) are in the ON state, whereby the transistors T_(i1) and T_(i3) are in the ON state by passing a bias current resulting from the bias voltage V_(b) between the base-emitter electrodes of the transistors T_(i1), T_(i3) in the vertical lines of the switches S_(b1), S_(b3). Accordingly, the current passing through the resistance R₁ to the transistors T₂₁, T₂₃, is passed out through the transistors T₂₁, T₂₃ and the diode D_(b) to the sustaining drive voltage terminal V_(s), whereby the turn-on pulse voltage is not applied to the output terminals E₂₁, E₂₃ by the voltage drop in the resistance R₁.

Thus, the transistor T_(i2) in the line of the switch S_(b2) is in the OFF state, since the base current is not passed. Accordingly, the turn-on pulse voltage is applied to the output terminal E₂₂, whereby the turn-on pulse voltage 7_(a) is applied to only the output terminal E₂₂.

In the same manner it is possible to apply the turn-on pulse 7_(a) to any desirable output terminal E_(ij) by selectively driving the first selective switch circuit S_(ai) and the second selective switch circuit S_(bj). The operation of applying the turn-off pulse 9_(a) is the same as the case applying the turn-on pulse 7_(a). In this case, the turn-off pulse 9_(a) (FIG. 2b) is applied to the turn-on voltage terminal V_(p).

FIG. 5 is a circuit diagram of another preferred embodiment of the display panel drive circuit of the AC drive discharge type display apparatus of the present invention. In this circuit, the second selective switch circuit S_(bj) for selecting the vertical lines of the matrix is connected between the base-emitter electrode of the transistors T_(ij). The operation of the drive circuit according to this embodiment will now be described as follows. In this circuit, the first selective switch circuit and the second selective switch circuit are usually in the OFF state, and the bias voltage is usually applied by the bias power source V_(b), through the resistance R₂ between the base-emitter electrodes of the transistor T_(ij) in the forward direction to the base-emitter junction.

Accordingly, the operation of applying the sustaining drive voltage 6_(a) (FIG. 2b) is similar to the embodiment of FIG. 4 and a drive waveform having an amplitude substantially equal and level to those of the sustaining drive voltage 6_(a) applied to the sustaining drive voltage terminal V_(s), is applied to the output terminal E_(ij).

The operation of applying the turn-on pulse 7_(a) to only the output terminal E₂₂ will be now described like that of FIG. 4. In this case, in a manner similar to the embodiment of FIG. 4, only the switch S_(a2) of the first selective switch circuit S_(ai) is in the ON state, and the collector electrode of the transistor T_(2i) in the transverse line is connected through the resistance R₁ to the turn-on voltage terminal V_(p). On the other hand, in the second selective switch circuit S_(bj), only switch S_(b2) is in the ON state, and the base-emitter electrodes of the transistors T_(i2) in the vertical line are connected in short-circuit, and the transistor T₁₂ is in the OFF state, since the base current is prevented from passing to the transistor T_(i2).

During this time period, the transistors T_(i1) and T_(i3) in the other vertical line are in the ON state by applying the bias voltage by the bias power source V_(b) in the forward direction of the base-emitter junction since the switches S_(b1) and S_(b3) are in the OFF state.

Accordingly, similar to the embodiment of FIG. 4, the turn-on pulse voltage 7_(a) is applied to only the output terminal E₂₂. Thus, in the same manner, it is possible to apply the turn-on pulse 7_(a) to a desirable terminal E_(ij) by selectively driving the first selective switch circuit S_(ai) and the second selective switch circuit S_(bj). The operation of applying the turn-off pulse 9a is similar to that of the turn-on pulse.

FIG. 6 is a circuit diagram of still another preferred embodiment of the display panel drive circuit of the AC drive discharge type display apparatus of the present invention. The drive circuit is to be used for driving the Y electrodes of the display panel, and the transistor T_(ij) is of the PNP type transistor. The operation of the drive circuit will be described below as follows. In this circuit, the first selective switch circuit S_(ai) is usually in the OFF state, and the second selective switch circuit S_(bj) is usually in the ON state. In this state, the sustaining drive voltage 6_(b) (FIG. 2c) is applied to the sustaining drive voltage terminal V_(s). When the positive voltage V_(s) is applied to the terminal V_(s) then the same is applied through the diode D_(a) to the emitter electrode of the transistor T_(ij). On the other hand, since the selective switch circuit S_(bj) is in the ON state, the bias voltage is applied by the bias power source V_(b) through the resistance R₂ between the base-emitter electrode of the transistor T_(ij) in the forward direction to the base-emitter junction, whereby the transistor T_(ij) is in the ON state.

Accordingly, the positive voltage V_(s) which is substantially equal to the emitter voltage is applied to the output terminal E_(ij) connected to the Y electrode of the display panel, that is the collector electrode of the transistor T_(ij), by the positive voltage applied to the emitter electrode of the transistor T_(ij).

When the terminal V_(s) becomes of a zero voltage, the zero voltage is applied through the diode D_(b) to the base electrode of the transistor T_(ij) whereby the bias in the forward direction is applied between the collector-base of the transistor T_(ij) and the voltage at the output terminal E_(ij), that is the collector electrode of the transistor T_(ij) is substantially equal to the zero voltage.

A drive waveform having a substantially equal level and pulse width to that of the sustaining drive voltage applied to the terminal V_(s) is applied to the output terminal E_(ij) which is connected to the collector electrode of the transistor, that is the Y electrode which is connected to it, when the first selective switch circuit S_(ai) is in the ON state and the sustaining drive voltage 6_(b) (FIG. 2c) is applied to the sustaining drive voltage terminal V_(s). The operation of applying the turn-on pulse to only the output terminal E₂₂ will now be explained.

In this case, similar to FIG. 4, only the switch S_(a2) in the first selective switch circuit S_(ai) is in the ON state, the collector electrode of the transistor T_(2j) is connected through the resistance R₁ to turn on voltage terminal V_(p) to which the turn-on pulse 7_(b) (FIG. 2c) is applied as an input. On the other hand, only the switch S_(b2) in the second selective switch S_(bj) is in the OFF state, whereby the transistors T_(2j) in the transverse line are in the OFF state.

Accordingly, the turn-on pulse 7_(b) is applied only to the output terminal E₂₂ similar to the embodiment of FIG. 4. In the same manner, it is possible to apply the turn-on pulse 7_(b) to a desired output terminal E_(ij) by selectively driving the first selective switch circuit S_(ai) and the second selective switch circuit S_(bi). The operation of applying and turn-off pulse 9_(b) (FIG. 2c) is similar to that of the turn-on pulse. In the embodiments of FIGS. 4, 5 and 6, it should be understood that the bias current is usually passed by the bias power source V_(b) in the forward direction to the base-emitter junction of the transistor T_(ij) in order to usually maintain the transistors T_(ij) in the ON state.

However, the period of time for maintaining the transistors T_(ij) in the ON state, can only be during the time period wherein the sustaining voltage is discharged to the sustaining drive voltage terminal V_(s) in the drive circuit using the NPN type transistors or the positive sustaining voltage is applied to the output terminal E in the drive circuit using the PNP type transistors and the turn-on pulse or the turn-off pulse are applied. Accordingly, it is possible to minimize the time period for passing the bias current by controlling to be in the ON state only during said period by connecting the bias power source in series to the switch circuit, or by controlling switch circuit S_(bi) in the ON state only during said period in the embodiment of FIG. 4 or FIG. 6. In this case, the consumption power of the bias source V_(b) can be advantageously decreased.

When the pulse voltage controlled to have a pulse width and level equal to that of the turn-on pulse 7 is applied to the turn-on voltage terminal V_(p), the maximum value of the width of the turn-on pulse is decided and the stability of the drive circuit is improved.

FIG. 7 is a circuit diagram of one embodiment of the input circuit of the turn-on or turn-off voltage in the drive circuits of FIGS. 4, 5 and 6. As shown in FIG. 7, the turn-on pulse is applied as an input through a diode D_(e) to the turn-on voltage terminal V_(p), and is added to the sustaining drive voltage 6 (FIG. 2a) by the capacitor C, whereby the voltage of the turn-on pulse applied to the turn-on voltage terminal V_(p) can be a low voltage provided by substracting the sustaining drive voltage

Thus, the direction of the diode D_(e) has been explained for the case of applying the positive voltage to the turn-on voltage terminal V_(p). When a negative voltage is applied, the direction of the connection is reversed to that of FIG. 7. The input of the turn-off voltage can be given in the same manner. In the embodiment wherein a short-circuit is connected between the base-emitter of the transistor T_(ij) by the selective switch circuit S_(bj) as shown in FIG. 5 an NPN type transistor is used. However, in the case where a PNP type transistor is used as the transistor T_(ij), it is possible to connect the short-circuit between the base-emitter of the transistor.

As it is now clear from the description, the present invention is to provide an AC drive discharge type display apparatus having a smaller number of circuit elements yet imparts the same function as that of the conventional apparatus which has many circuit elements.

Obviously numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described herein. 

What is claimed as new and desired to be secured by letters patent is:
 1. An AC drive discharge type display apparatus which comprises:a display panel for housing groups of traverse electrodes and vertical electrodes positioned in cross form with a gap therebetween, cross points of the groups of traverse electrodes and vertical electrodes being made luminescent by applying a turn-on signal and being turned-off by applying a turn-off signal; a plurality of transistors disposed in a matrix, the collectors of the transistors being connected to corresponding electrodes of the display panel; means for commonly connecting the base of the transistor in each traverse line of the matrix to a sustaining drive voltage source; means for commonly connecting the emitters of the transistors in each traverse line of the matrix; means for commonly connecting through resistances the collectors of the transistors in each vertical line of the matrix; a first selective switch means for applying the turn-on signal or the turn-off signal to the means for commonly connecting the collectors of the specific vertical line of the matrix and a second selective switch means for turning-on the transistor through the means for commonly connecting the emitter and the means for commonly connecting the base of a traverse line other than the specific one, by applying forward bias voltage across the base-emitter of the transistor of the traverse line other than the specific one, whereby the turn-on signal or the turn-off signal is applied through the collector of the transistor disposed at the cross point of the specific vertical line selected by the first selective switch means and the specific traverse line selected by the second selective switch means, to the electrode of the display panel connected to the collector to make the cross point luminescent and nonluminescent.
 2. An AC drive discharage type display apparatus according to claim 1, which comprises a circuit for discharging the charge of the electrodes of the display panel between the commonly connected emitters of the transistors in each traverse line of the matrix and the sustaining drive voltage source when the instantaneous value of the sustaining voltage equals zero voltage. 